Tumor Progression Locus 2 (Map3k8) Is Critical for Host Defense againstListeria monocytogenesand IL-1β Production

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Tumor progression locus 2 (Tpl2, also known as Map3k8 and Cot) is a serine-threonine kinase critical in innate immunity, linking toll-like receptors (TLRs) to TNF production through its activation of ERK. Tpl2(-/-) macrophages have abrogated TNF production but overproduce IL-12 in response to TLR ligands. Despite enhanced IL-12 production, Tpl2(-/-) T cells have impaired IFN-gamma production. Therefore, the role of Tpl2 in a bona fide bacterial infection where all of these cytokines are important in host defense is unclear. To address this issue, we infected Tpl2(-/-) mice with the model pathogen Listeria monocytogenes. We found that Tpl2(-/-) mice infected i.v. with L. monocytogenes had increased pathogen burdens compared with wild-type mice and rapidly succumbed to infection. Enhanced susceptibility correlated with impaired signaling through TLR2 and nucleotide-binding oligomerization domain 2, two receptors previously shown to mediate Listeria recognition. Surprisingly, TNF production in response to infection was not significantly impaired, even though Tpl2 has been implicated in the regulation of TNF. We found that the role of Tpl2 has cell-type specific effects in regulating TNF and transduces signals from some, but not all, pattern recognition receptors (PRR). In contrast to the cell-type- and receptor-specific regulation of TNF, we found that Tpl2 is essential for IL-1beta production from both macrophages and dendritic cells. These studies implicate Tpl2 as an important mediator for collaboration of pattern recognition receptors with danger-associated molecular patterns to induce TNF and IL-1beta production and optimal host defense.